Digital Microphone AGC Compensation for PDM Dynamic Range
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Solution Overview
Problem
Digital microphone devices with fixed preamplifier gain have limited dynamic range due to the lack of external control signals, restricting the optimization of the analog-to-digital conversion path and compliance with standard pin configurations.
Innovation Solution
A digital microphone device with internal gain control capabilities, featuring a variable gain preamplifier, Automatic Gain Controller, and compensation block, which generates a single-bit Pulse Density Modulation output signal by adjusting the gain and compensating for signal variations internally.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed gain preamplifier is used to simplify the device structure, then the device complexity is reduced, but the dynamic range is limited
Solution Approach 1:
The preamplifier automatically adjusts its own gain based on the detected output signal level. The gain control voltage is generated internally by detecting the output signal and applying negative feedback through a control loop, eliminating the need for external control signals or additional pins.
Solution Approach 2:
A feedback loop is implemented where the output signal of the preamplifier is detected and used to generate a gain control voltage that adjusts the preamplifier gain. This automatic feedback mechanism enables dynamic range extension without requiring external control circuits.
2Quantity of substance
If no external control pins are provided to comply with standard pin configuration, then the pin count is reduced, but the ability to control internal path gain is lost
Solution Approach 1:
The preamplifier automatically adjusts its own gain based on the detected output signal level. The gain control voltage is generated internally by detecting the output signal and applying negative feedback through a control loop, eliminating the need for external control signals or additional pins.
3Device complexity
If the preamplifier gain is fixed, then the device structure is simplified, but the analog to digital conversion path noise cannot be optimized
Solution Approach 1:
The preamplifier gain is made dynamically adjustable through automatic gain control. The gain varies automatically based on the input signal level, allowing optimization of the signal-to-noise ratio for different operating conditions without requiring complex external control systems.
Solution Approach 2:
A feedback loop is implemented where the output signal of the preamplifier is detected and used to generate a gain control voltage that adjusts the preamplifier gain. This automatic feedback mechanism enables dynamic range extension without requiring external control circuits.
Data Source
AI summary
The present disclosure refers to a digital microphone device providing a single-bit Pulse Density Modulation PDM output signal. The digital microphone comprises a microphone, arranged to convert an acoustic input signal into an analog electrical signal, and a preamplifier, having a variable gain, arranged to receive the analog electrical signal and to provide an amplified analog electrical signal, depending on the variable gain. The variable gain depends on a gain control signal. The digital microphone further comprises an Analog-to-Digital Converter block, arranged to receive the amplified analog electrical signal and to convert it into a respective digital signal; and a compensation block, arranged to receive the digital signal and to perform a digital operation on such digital signal, on the basis of a compensation signal, to generate a compensated signal. Furthermore, the digital microphone comprises an Automatic Gain Controller block 25, arranged to detect the digital signal and to generate said gain control signal, on the basis of the detected digital signal. The Automatic Gain Controller block is further arranged to generate the compensation signal, on the basis of the control signal, and to provide the compensation signal to the compensation block, to compensate a variation of the digital signal resulting from the variable gain of the preamplifier. Finally, the digital microphone device comprises a conversion block, arranged to receive the compensated signal and to convert it into the single-bit PDM output signal.